The invention pertains to a ceramic material, as well as a method of making the same, that contains silicon aluminum oxynitride (SiAlON) and ytterbium.
SiAlON materials have a number of uses such as, for example, cutting inserts for various metal cutting application and wear parts for various wear applications (e.g., plunger rods for pumps, plunger ball blanks, down hole pump check valve blanks, bushings, blast nozzles, and other wear and impact applications). Exemplary patents that disclose SiAlON materials are U.S. Pat. Nos. 4,563,433 and 4,711,644. One article that discusses SiAlON materials is Izhevskiy et al., xe2x80x9cProgress in SiAlON ceramics, Journal of the European Ceramic Society 20 (2000) pages 2275-2295.
SiAlON materials may contain an alpha prime (or alphaxe2x80x2) phase and a beta prime (or betaxe2x80x2) phase and one or more other phases such as, for example, a glassy phase and/or a crystalline phase. The alpha prime SiAlON phase may be of the formula MxSi12xe2x88x92(m+n)Alm+nOnN16xe2x88x92n where M is Li, Ca, Y or other lanthanides and where the theoretical maximum of x is 2, the value of n ranges between greater than 0 and less than or equal to 2.0, and the value of m ranges between greater than or equal to 0.9 and less than or equal to 3.5. The beta prime SiAlON phase may be of the formula Si6xe2x88x92zAlzOzN8xe2x88x92z where 0 less than zxe2x89xa64.2. In the case where M is yttrium, the crystalline phases may include YAG (yttrium aluminum garnet) which is a cubic phase of the formula Y3Al5O12); YAM which is a monoclinic phase of the formula Y4Al2O9; Nxe2x80x94YAM which is a monoclinic phase of the formula Y4Si2O7N2; and Y-N-xcex1-Wollastonite which is a monoclinic phase of the formula YSiO2N.
SiAlON materials may comprise an alpha prime SiAlON phase and a beta prime SiAlON phase, as well as further contain silicon carbide particles dispersed throughout the SiAlON matrix. Such a SiAlON material is disclosed in U.S. Pat. No. 4,826,791 to Mehrotra et al.
Other ceramic materials include an alpha prime SiAlON phase, a beta SiAlON phase and an intergranular phase wherein the ceramic optionally contains refractory phases. The ceramic material has an alloyed surface with a higher oxygen and aluminum content. U.S. Pat. No. 4,880,755 to Mehrotra et al. discloses such a ceramic material.
U.S. Pat. No. 5,370,716 to Mehrotra et al. discloses a high Z-SiAlON material comprising beta prime SiAlON phase. The beta prime SiAlON phase has a formula Si6xe2x88x92zAlzOzN8xe2x88x92z where 1 less than z less than 3.
U.S. Pat. No. 5,908,798 to Chen et al. discloses a SiAlON material wherein the focus is on the reinforcement of alpha prime SiAlON with elongated grains of alpha prime SiAlON. The examples that include ytterbium produce a material with only alpha prime SiAlON phase that does not contain any beta prime SiAlON phase.
U.S. Pat. No. 6,124,225 to Tien et al. focuses upon the use of gadolinium (Gd) in a SiAlON material to produce an alpha prime SiAlON material that is reinforced by elongated grains of alpha prime SiAlON.
Although current SiAlON cutting inserts exhibit acceptable properties (e.g., hardness, toughness, thermal shock resistance) it would be desirable to provide for an improved SiAlON material that has application as a cutting insert that exhibits improved metal cutting performance properties including hardness, Young""s modulus, toughness, thermal conductivity, and thermal shock resistance. The same is true for SiAlON wear parts in that although current SiAlON wear parts have acceptable properties (e.g., hardness, Young""s modulus, toughness, thermal conductivity, and thermal shock resistance), it would be desirable to provide an improved SiAlON material that has application as a wear part that exhibits improved properties.
In one form thereof, the invention is a sintered ceramic body made from a starting powder mixture that includes silicon nitride powder. Less than or equal to about 5 weight percent of the starting silicon nitride powder comprises beta-silicon nitride. The ceramic body comprises a two phase composite of alpha prime SiAlON phase and beta prime SiAlON phase. The alpha prime SiAlON phase contains ytterbium therein. The alpha prime SiAlON phase is present in an amount between about 25 weight percent and about 85 weight percent of the two phase composite.
In still another form thereof, the invention is a ceramic composition that comprises a two phase composite of alpha prime SiAlON phase and beta prime SiAlON phase. The alpha prime SiAlON phase has ytterbium therein. The alpha prime SiAlON phase is present in an amount between about 45 weight percent and about 85 weight percent of the two phase composite. The composition further includes an intergranular phase.
In another form thereof, the invention is a ceramic composition that consists essentially of an alpha prime SiAlON phase and a beta prime SiAlON phase. The alpha prime SiAlON phase has ytterbium therein. The alpha prime SiAlON phase is present in an amount between about 45 weight percent and about 85 weight percent of the total content of the alpha prime SiAlON phase and the beta prime SiAlON phase. The beta prime SiAlON phase is present in an amount between about 15 weight percent and about 55 weight percent of the total content of the alpha prime SiAlON phase and the beta prime SiAlON phase. The composition further includes an intergranular phase wherein the intergranular phase includes one or more of a glassy phase and an intergranular crystalline phase.
In still another form thereof, the invention is a sintered ceramic body made from a starting powder mixture wherein the starting powder mixture includes silicon nitride powder. Less than or equal to about 2 weight percent of the starting silicon nitride powder comprises beta-silicon nitride. The sintered ceramic body comprises a two phase composite of an alpha prime SiAlON phase and a beta prime SiAlON phase. The alpha prime SiAlON phase has ytterbium therein. The alpha prime SiAlON phase is present in an amount greater than about 25 weight percent of the two phase composite. The composition further includes an intergranular phase.
In yet another form thereof, the invention is a ceramic composition that comprises a two phase composite of an alpha prime SiAlON phase and a beta prime SiAlON phase. The alpha prime SiAlON phase has therein one or more elements selected from the group consisting of ytterbium, erbium, thulium, scandium and lutetium. The alpha prime SiAlON phase is present in an amount between about 45 weight percent and about 85 weight percent of the two phase composite. The ceramic composition further includes an intergranular phase.
In still another form thereof, the invention is a sintered ceramic body made from a starting powder mixture that includes silicon nitride powder, wherein the starting silicon nitride powder comprising less than or equal to about 2 weight percent beta-silicon nitride. The ceramic body comprises a two phase composite that includes an alpha prime SiAlON phase containing ytterbium therein and a beta prime SiAlON phase. The composition of the ceramic body falls above the line xxe2x80x94x in FIG. 5.
In another form thereof, the invention is a sintered ceramic body made from a starting powder mixture that includes silicon nitride powder, wherein the starting silicon nitride powder comprising less than or equal to about 5 weight percent beta-silicon nitride. The ceramic body comprises a two phase composite that includes an alpha prime SiAlON phase and a beta prime SiAlON phase. The alpha prime SiAlON phase contains one or more rare earth elements therein, and wherein for a valence of +3 and a coordination number of 6 the effective ionic radius of each one of the rare earth elements equals less than 0.900 Angstroms. The alpha prime SiAlON phase is present in an amount greater than or equal to about 25 weight percent of the two phase composite.